A conventional active matrix liquid-crystal (hereinafter also referred to as `LC`) display device with thin-film transistor(TFT) substrate will be explained below, referring to FIG. 1. This device, as shown in FIG. 1B, has the structure that a twist-nematic liquid-crystal layer 620 is sandwiched between a TFT substrate 630 and a color filter (CF) substrate 610. The TFT substrate 630 has the structure that, on a TFT glass substrate 104, a gate electrode 105, gate insulating film 107, a-Si layer 109, n+a-Si layer 110, a source electrode 112 and drain electrode 111, a pixel electrode 631, and passivation film 632 are formed in this order. As the passivation film 632, SiN film of about 300 nm thick made by plasma CVD is typically used. On the other hand, the CF substrate 610 has the structure that a black matrix 612, color layer 613 and an opposing electrode 614 are formed, in this order, on a CF glass substrate 611.
In such an active matrix liquid-crystal display device as composed above, it is necessary to the black matrix 612 so as to shield light through a light-leaked region B. Therefore, by reason that it is necessary to estimate an overlap margin of this light-shielding part, a light-transmitted region A of the LC display panel is reduced. Thus, there is the problem that the transmissivity of the entire device is reduced.
So, means for enlarging the light-transmitted region, i.e., means for enhancing the aperture ratio is proposed, e.g., Japanese patent application laid-open No.9-152625 (1997). This device has, as show in FIG. 2A, the structure that the pixel electrode 631, data line 602 and gate line 601 are overlapped. In such an active matrix liquid-crystal display as thus composed, it is necessary to form interlayer insulating film 701 by using a material with low permittivity and possible to thicken so as to reduce the overlap capacity of the pixel electrode 631, data line 602 and gate line 601. For example, used is interlayer insulating film where 2 to 4 .mu.m thick positive type photosensitive acrylic resin with specific permittivity .epsilon.=3.0 is laminated on inorganic film of SiN conventionally used.
The method of making the interlayer insulating film 701 will be explained below, referring to FIGS. 3A to 3D. Like conventional methods, SiN layer 102 of about 300 nm thick is laminated by plasma CVD, forming a contact hole 113 by patterning (FIG. 3A) . Then, after coating it with photosensitive acrylic resin, patterning is conducted by pre-baking, exposure and alkali-development (FIGS. 3B and 3C). Then, UV light including i line is radiated all over the surface to decolorize into transparent film. Then, the resin is hardened by thermal cross-linking reaction. Then, transparent film such as ITO is formed by sputtering, patterned into the pixel electrode 631 (FIG. 3D). Finally, it is annealed at 250.degree. C. for about 30 min.
In the active matrix liquid-crystal display device with TFT substrate thus obtained, there is no light-leaked region, and therefore the black matrix is not necessary. Therefore, the numerical aperture can be enhanced.
However, in the conventional method, the layer formation and patterning are conducted for each of the SiN layer and organic film. Also, after patterning of organic film by wet-etching, it is desired that dry-etching is conducted to remove the remaining resin that may cause a failure in contact. Due to these, the number of processes is increased. Thus, there are problems in working property and productivity.
To prevent the increase in the number of processes to enhance the productivity, it might be suitable that the processes are conducted in the lump as much as possible. For example, after forming the SiN layer and organic film and then wet-etching the organic film, dry-etching of base layer can be conducted using the obtained organic film pattern as a mask. However, the positive type photosensitive acrylic resin lacks in resistance to dry-etching, and therefore its surface is significantly worn out by dry-etching. Therefore, such a method cannot be applied.
Also, there is the problem that the near i-line optical transmissivity of positive type photosensitive acrylic resin is low. Also, the thermal resistance of photosensitive group is not sufficient and the transmissivity is therefore like to further reduce due to the thermal treatment such as annealing in post-process. Therefore, the performance of TFT(thin-film transistor) substrate is deteriorated.